Two Rod and Valve Gear Questions

Mon Aug 6 10:21:05 EDT 2018

This was also an area for dabbling by various steam loco engineers and designers in the UK.

Most UK  2-cylinder locos were at 90 or 120 degrees. How much real difference this made in reality (fuel economy, maintenance etc.) is difficult to determine. Late series Britannia Pacifics were always deemed to be rough riding. By the same token some multi-cylinder locos were just as rough (Royal Scot 7Ps, Peppercorn A1s etc.) whilst others rode very smoothly. The A4 Mallard type was always deemed to be a very smooth running loco design with three cylinders a derived/conjugated valve gear for the inside cylinder. 

Regards

Phil Mortimer

From: NW-Mailing-List [mailto:nw-mailing-list-bounces at nwhs.org] On Behalf Of NW Mailing List
Sent: Monday, August 6, 2018 1:44 PM
To: NW Mailing List
Subject: Re: Two Rod and Valve Gear Questions

The ratio between the distance of the main pin from the axle center varied from engine design to engine design.  It would be different from, say, the Y-6 and the J – both engines had 32-inch strokes but a foot difference in driver diameters (assuming new tires).  

The normal practice in American railroading was right-hand lead.  The PRR was the notable exception to this; they used left-hand lead.  It was known that the side that had the lead pounded the track more than the other; one theory has it that PRR wanted the left-hand side to pound the roadbed harder because ot a preponderance of multiple-track railroading; the left side of the roadbed would be stronger.  The quarter was the standard for two-cylinder locomotives, assuring the most even distribution of torque during the rotation of the wheel.  Three-cylinder locomotives typically used a 120-degree ratio instead of a quarter.  The exception to this is the Baldwin 60000 three-cylinder 4-10-2 displayed at the Franklin Institute in Philly.  It’s drivers are quartered, but the third cylinder is 135 degrees from both the outer crankpins.  

Hope this helps.

EdKing

From: NW Mailing List 

Sent: Monday, August 06, 2018 6:16 AM

To: N&W Mailing List 

Subject: Two Rod and Valve Gear Questions

Hopefully there will be some talent left around which can give an answer to these two humble little questions...

(1)  Is there always a mathematical ratio of 2:1 between (a) the distance from center of axle to center of main driving crank pin, on the one hand,  and (b) the length of the stroke of the piston, on the other hand?  (Prima facie, this sounds like a really, really dumb question... sorry.)

(2)  In quartering drivers on axles, how far in degrees is one driver advanced beyond perfect quarter, to insure that the engine will never be caught on dead-center?  (And I believe N&W used right-hand lead, contrary to most American practice, did they not?  If so, I wonder where that practice came from?)

--  abram burnett, 

(who should probably just stick to turnip farming...)

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